The present invention relates to a driver IC and an LED (light emitting diode) print head which can be incorporated into an electrophotographic printer, a copying machine, a facsimile machine and the like. The LED print head hereinafter also means a device which includes a light emitting transistor and a liquid crystal shutter.
FIG. 1 is a circuit diagram showing a conventional LED print head, and FIG. 2 is a timing chart showing signals inputted to the LED print head of FIG. 1.
As shown in FIGS. 1 and 2, in the LED print head 1, drive data DATA.sub.1 for one line of LED elements 7 are transmitted to a shift register 3 of a driver IC 2 (between a time t.sub.1 and a time t.sub.2) in synchronization with a clock signal CLK, and subsequently transmitted to a latch circuit 4 (at a time t.sub.3) in synchronization with a load signal LD.sub.1. Drive signals based on the drive data DATA.sub.1 are then transmitted to the LED elements 7 of an LED array 6 (at a time t.sub.5) through AND elements 5 and wires 8, respectively, so that one line of LED elements 7 are simultaneously operated. Such a driving system is called a static system.
However, in the above-described LED print head 1, the LED elements 7 are connected to the AND elements 5 by the wires 8, respectively. Therefore, a large number of wires 8 are needed (for example, 4992 wires are needed in the case of an LED print head for forming an image with a dot density of 600 [DPI] on a sheet of A4-size paper) and a density of the wires 8 is increased, so manufacturing costs of the LED print head 1 are raised.
Further, FIG. 3 is a circuit diagram showing another conventional LED print head, and FIG. 4 is a timing chart showing signals inputted to the LED print head of FIG. 3.
As shown in FIGS. 3 and 4, in the LED print head 11, drive data DATA.sub.2 for 1/2 line of LED element groups 17 ("odd-numbered LED elements 17a") are transmitted to a shift register 13 of a driver IC 12 (between a time t.sub.11 and a time t.sub.12) in synchronization with a clock signal CLK.sub.2, and subsequently transmitted to a latch circuit 14 (at a time t.sub.13) in synchronization with a load signal LD.sub.2. Drive signals based on the drive data DATA.sub.2 are then transmitted to the LED elements 17a of an LED array 16 (at a time t.sub.15) through AND elements 15 and wires 18, respectively. Since only LED grounds in the odd-numbered LED elements 17a are grounded through the ground line 10a (at a time t.sub.14), i.e., only the odd-numbered LED elements 17a are in a light emission enabling state, light is emitted from only the odd-numbered LED elements 17a. Next, drive data DATA.sub.2 for 1/2 line of LED element groups 17 ("even-numbered LED elements 17b") are transmitted to the shift register 13 (between a time t.sub.16 and a time t.sub.17) in synchronization with the clock signal CLK.sub.2, and subsequently transmitted to the latch circuit 14 (at a time t.sub.18) in synchronization with the load signal LD.sub.2. Drive signals based on the drive data DATA.sub.2 are then transmitted to the LED elements 17b of the LED array 16 (at a time t.sub.20) through the AND elements 15 and the wires 18, respectively. Since only LED grounds in the even-numbered LED elements 17b are grounded through the ground line 10b (at a time t.sub.19), i.e., only the even-numbered LED elements 17b are in a light emission enabling state, light is emitted from only the even-numbered LED elements 17b. In the LED print head 11, the odd-numbered LED elements 17a and the even-numbered LED elements 17b are driven alternately. Such a driving system is called a dynamic system.
In the LED print head 11, couples of two adjacent LED elements 17a, 17b are connected to the AND elements 15 by the wires 18, respectively. Therefore, a number of the wires 18 can be reduced by half in comparison with the LED print head 1 as the static system shown in FIG. 1.
However, in comparison with the LED print head 1 of FIG. 1 and the LED print head 11 of FIG. 3, the drive data DATA.sub.1 and DATA.sub.2, the load signals LD.sub.1 and LD.sub.2, etc. are different from each other. Therefore, the LED print head shown in FIG. 3 having a small number of wires between the LED array and the driver IC cannot be incorporated into an LED printer adopting a data transfer system (data transfer system using the drive data DATA.sub.1 and the load signal LD.sub.1) shown in FIG. 2.